Magnetoresistive element

Abstract

According to one embodiment, a magnetoresistive element includes first, second and third magnetic layers, and first and second nonmagnetic layers. The third magnetic layer has stack layers including a first stack layer close to the second magnetic layer, and a second stack layer far from the second magnetic layer. Each of the first and second stack layers includes a first layer made of a ferromagnetic material and a second layer made of a nonmagnetic material, and a first ratio of a film thickness of the first layer to that of the second layer in the first stack layer is higher than a second ratio of a film thickness of the first layer to that of the second layer in the second stack layer.

What is claimed is: 
     
       1. A magnetoresistive element comprising:
 a first magnetic layer; 
 a second magnetic layer; 
 a third magnetic layer; 
 a first nonmagnetic layer formed between the first magnetic layer and the second magnetic layer; and 
 a second nonmagnetic layer formed between the second magnetic layer and the third magnetic layer, 
 wherein: 
 the third magnetic layer has a structure in which stack layers are stacked, 
 the stack layers include a first stack layer close to the second magnetic layer, and a second stack layer which is farther from the second magnetic layer than the first magnetic layer is, 
 each of the first stack layer and the second stack layer includes a first layer made of a ferromagnetic material and a second layer made of a nonmagnetic material, 
 a first ratio of a film thickness of the first layer to a film thickness of the second layer in the first stack layer is higher than a second ratio of a film thickness of the first layer to a film thickness of the second layer in the second stack layer, 
 a saturation magnetization of the first stack layer is larger than a saturation magnetization of the second stack layer, and 
 an anisotropic magnetic field of the second stack layer is larger than an anisotropic magnetic field of the first stack layer. 
 
     
     
       2. The element according to  claim 1 , wherein the first layer is positioned on a side close to the second magnetic layer, and the second layer is positioned on a side far from the second magnetic layer. 
     
     
       3. The element according to  claim 1 , wherein the first layers and the second layers are alternately arranged in the third magnetic layer. 
     
     
       4. The element according to  claim 1 , wherein:
 the third magnetic layer includes a first stack in which a plurality of the first stack layers are stacked, and a second stack in which a plurality of the second stack layers are stacked, 
 the first stack layers in the first stack have a same first ratio, and 
 the second stack layers in the second stack have a same second ratio. 
 
     
     
       5. The element according to  claim 1 , wherein:
 the first layer of the first stack layer and the first layer of the second stack layer have a same film thickness, and 
 a film thickness of the second layer of the first stack layer is smaller than a film thickness of the second layer of the second stack layer. 
 
     
     
       6. The element according to  claim 1 , wherein:
 a film thickness of the first layer of the first stack layer is larger than a film thickness of the first layer of the second stack layer, and 
 the second layer of the first stack layer and the second layer of the second stack layer have a same film thickness. 
 
     
     
       7. The element according to  claim 1 , wherein:
 a film thickness of the first layer of the first stack layer is larger than a film thickness of the first layer of the second stack layer, and 
 a film thickness of the second layer of the first stack layer is smaller than a film thickness of the second layer of the second stack layer. 
 
     
     
       8. The element according to  claim 1 , wherein:
 a film thickness of the first layer is larger than a film thickness of the second layer in the first stack layer, and 
 a film thickness of the first layer is smaller than a film thickness of the second layer in the second stack layer. 
 
     
     
       9. The element according to  claim 1 , wherein the first magnetic layer is a storage layer, and the second magnetic layer is a reference layer. 
     
     
       10. The element according to  claim 1 , wherein:
 the ferromagnetic material is an alloy containing not less than one element selected from the group consisting of cobalt (Co), iron (Fe), and nickel (Ni), and 
 the nonmagnetic material is an alloy containing not less than one element selected from the group consisting of platinum (Pt), palladium (Pd), terbium (Tb), ruthenium (Ru), chromium (Cr), iridium (Ir), rhodium (Rh), osmium (Os), rhenium (Re), gold (Au), and copper (Cu). 
 
     
     
       11. A magnetoresistive element comprising:
 a first magnetic layer; 
 a second magnetic layer; 
 a third magnetic layer; 
 a first nonmagnetic layer formed between the first magnetic layer and the second magnetic layer; and 
 a second nonmagnetic layer formed between the second magnetic layer and the third magnetic layer, 
 wherein: 
 the third magnetic layer has a structure in which stack layers are stacked, 
 each of the stack layers includes a first layer made of a ferromagnetic material and a second layer made of a nonmagnetic material, 
 the third magnetic layer has a first surface close to the second magnetic layer and a second surface which is farther from the second magnetic layer than the first surface is, 
 a ratio of a composition of the ferromagnetic material to a composition of the nonmagnetic material on the first surface of the third magnetic layer is higher than a ratio of the composition of the ferromagnetic material to the composition of the nonmagnetic material on the second surface of the third magnetic layer, 
 a saturation magnetization on the first surface of the third magnetic layer is larger than a saturation magnetization on the second surface of the third magnetic layer, and 
 an anisotropic magnetic field on the second surface of the third magnetic layer is larger than an anisotropic magnetic field on the first surface of the third magnetic layer. 
 
     
     
       12. The element according to  claim 11 , wherein the first layer is an alloy layer made of an alloy containing the ferromagnetic material and the nonmagnetic material. 
     
     
       13. The element according to  claim 11 , wherein a concentration of the ferromagnetic material in the third magnetic layer is higher on the first surface than on the second surface, and a concentration of the nonmagnetic material in the third magnetic layer is higher on the second surface than on the first surface. 
     
     
       14. The element according to  claim 11 , wherein a concentration of the ferromagnetic material on a surface of the stack layer on a side of the third magnetic layer, which is close to the second magnetic layer, is higher than a concentration of the ferromagnetic material on a surface of the stack layer on a side of the third magnetic layer, which is far from the second magnetic layer. 
     
     
       15. The element according to  claim 11 , wherein the first magnetic layer is a storage layer, and the second magnetic layer is a reference layer. 
     
     
       16. The element according to  claim 11 , wherein:
 the ferromagnetic material is an alloy containing not less than one element selected from the group consisting of cobalt (Co), iron (Fe), and nickel (Ni), and 
 the nonmagnetic material is an alloy containing not less than one element selected from the group consisting of platinum (Pt), palladium (Pd), terbium (Tb), ruthenium (Ru), chromium (Cr), iridium (Ir), rhodium (Rh), osmium (Os), rhenium (Re), gold (Au), and copper (Cu). 
 
     
     
       17. A magnetoresistive element comprising:
 a first magnetic layer; 
 a second magnetic layer; 
 a third magnetic layer; 
 a first nonmagnetic layer formed between the first magnetic layer and the second magnetic layer; and 
 a second nonmagnetic layer formed between the second magnetic layer and the third magnetic layer, 
 wherein: 
 the third magnetic layer has a structure in which stack layers are stacked, 
 each of the stack layers includes a first layer made of a ferromagnetic material and a second layer made of a nonmagnetic material, 
 the third magnetic layer has a first surface close to the second magnetic layer and a second surface which is farther from the second magnetic layer than the first surface is, 
 a saturation magnetization on the first surface of the third magnetic layer is larger than a saturation magnetization on the second surface of the third magnetic layer, and 
 an anisotropic magnetic field on the second surface of the third magnetic layer is larger than an anisotropic magnetic field on the first surface of the third magnetic layer. 
 
     
     
       18. The element according to  claim 17 , wherein a saturation magnetic moment on the first surface of the third magnetic layer is larger than a saturation magnetic moment on the second surface of the third magnetic layer.